1. Field of the Invention
This invention relates to a method and an apparatus for sweeping overflowed resin on a semiconductor device manufacturing process, particularly to a method and an apparatus for sweeping overflowed resin stuck in between leads in resin-sealing the semiconductor device.
2. Description of the Related Art
Resin is injected in a cavity of a semiconductor device package in a resin sealing process on the semiconductor device manufacturing process. FIG. 1 is a perspective view showing a semiconductor device for which such a resin sealing process is finished.
The lead frame 21 is provided with a plurality of leads 21A protruded in one or a plurality of directions and dam bars 21B for connecting those leads 21A. A semiconductor chip wire-bonded to a plurality of the leads 21A is sealed by thermosetting resin in the package 20. As the thermosetting resin, generally biphenyl epoxy resin is used. In FIG. 1, Fr indicates the top side of the package 20.
In resin sealing, unhardened state resin often leaks from a gap between upper and lower dies corresponding to the thickness of the lead frame 21A positioned between those dies. Leaked resin is then filled in openings like quadrate slots formed with boundaries of the package 20, the leads 21A, and the dam bar 21B and hardened by three-dimensional crosslinking as it is cooled down, resulting in forming of overflowed resin 25. This overflowed resin 25 is removed using a pressing machine, etc. after the resin sealing process is ended.
FIG. 2 is a cross sectional view showing such a related art apparatus for sweeping overflowed resin. FIG. 3 explains how the overflowed resin is swept using a related art method of sweeping overflowed resin on the semiconductor device manufacturing proces. FIG. 4 is a view explaining the end of the overflowed resin sweeping. FIG. 5 is a cross sectional view of a state after overflowed resin is swept using a related art method. Hereunder, how to sweep the overflowed resin from a semiconductor device will be explained with reference to those drawings.
In FIG. 2, the overflowed resin sweeping apparatus 50 of the pressing machine structure comprises a punch holder base 52 moving up/down according to the up/down motion of a shank 51 as shown by an arrow mark V10; a punch 54 built in the punch holder base 52 so as to be protruded downward and energized by a spring 53 for being pressed; and a base frame 56 provided with an approximately U-shaped lead frame holder 55 on its top and away from the punch holder base 52 downward.
The package 20 in which a semiconductor chip is sealed by resin is inserted in between the punch holder base 52 and the base frame 56 so that two leads 21A can respectively come in contact with both tips of the approximately U-shaped lead frame holder 55. In this state, the overflowed resin 25 between those leads 21A still remains inside both tips of the lead frame holder 55.
At this time, the punch holder base 52 is driven by the shank 51 to go down in the direction of the arrow mark V12 (moving toward the punch) so that the tip of the punch contacts the overflowed resin 25, then it is pressed against the resin 25 strongly to make the resin 25 be separated from the side wall surface of the lead frame 21 and be discharged as punched resin 60.
To prevent resin (not separated yet) from remaining on the side wall surfaces of the package, the leads, etc. at this time, the clearances from the package, the leads, and the punch must be minimized and the positions of the punch, the package, and the leads must be controlled properly to achieve the object. This is so difficult, however, as to be almost impossible under the present circumstances. Furthermore, if the above clearance is small, the punch comes in contact with both the package and the leads even by a very small positional error, resulting in partial damage of the leads.
In related art techniques, an attempt is made to design the tip of the punch 54 smaller than the gap between leads, that is, smaller than the size of overflowed resin 25 to prevent such a problem.
As a result, the punch 54 contacts the upper side (Fr side in FIG. 3) of overflowed resin 25 and presses it down to generate a stress inside the overflowed resin 25, so that the stress concentration is induced at ends P1 and P2 of the punch 54. Furthermore, the stress concentration is induced at the lower end P3 of the boundary Cs between the package 20 and the overflowed resin 25, as well as at the lower end P4 of the boundary Bs between the dam bar 21B and the overflowed resin 25. The stress .sigma.12 in the overflowed resin 25 is concentrated on the face 62 between the end P1 and the lower end P3, and on the face 63 between the end P2 and the lower end P4, respectively.
When the punch 54 further goes down, the stress reaches the breaking stress due to a static load to generate a crack on the faces 62 and 63 of the overflowed resin or in the neighbourhood thereof along a three-dimensional crosslinked chain and results in a brittle rupture. In other words, such a crack grows into a rupture face so that the overflowed resin 25 is ruptured and the ruptured resin 60 is separated from the lead frame 21 and dropped away as shown in FIG. 4.
In the above related art techniques for sweeping the overflowed resin, however, unseparated resin 61 is left on the side wall surfaces of the package and each lead as shown in FIG. 4 and FIG. 5. This is because a crack occurs from the side of the cutting edge of the punch as mentioned above before a shear stress between side wall surfaces of the package and the lead increases around the upper end of the boundary of overflowed resin 25.
This residual resin drops off in a subsequent process or after product delivery to be foreign matters which cause an accident due to imperfect operation of an apparatus using the device, or a problem of product quality deterioration, etc.